Aircraft engine mount



July 29, 1952 J, M, TYLER Y2,605,062

AIRCRAFT ENGINE MOUNT Filed 001'.. 2, 1947 [n @en Zo? Joz M 7192er @H 4MM Patented July 29, 1952 SUNjI TED TATES PATENT' OFFICE mi .j 1 .La ,Y Y. 7,.'.72695062 A y.

v eAi'acnArrENolNi: Mourir l John M. Tyler, West Hartford, Conn., assigner to United Aircraft Corporation, East Hartford,

Conn., a corporation of Delaware Application october 2,1947,'ser`ialN0.77i,525

irrespective of g loads or maneuver acceleration loads: ,Thus, the compressivefaxesf the mount uintsare'solocated and the stiffnesstratios of the to improvements in enunits. are;so chosenthat the distance from the` elasticpenter of the mounting system to. `the center of gravity 'ofthe power plant and the distance from the :elasticcenter to 'a selected point, which it is desired to maintain stationary, ,are so related with respect to each other and with respect to the translational stiffness and rotational stiffness of the mounting system at and around the elastic center of the system that the selected point is maintained stationary during lateral deiiections ofthe power plant.` The elastic center ofthe system isthe point atwhich the applicaf tion of a lforce will causepure translation of the power plant and which lies on the axisabout which the power plant will rotate when a couple is applied thereto.

The invention is particularly intended to provide a resilient mounting means for an aircraft power plant capable of maintaining `the align.- ment of ajpower take-oifat therearvof the power plant'withrespect to a'diven' member carried-by fixed'v airplaneistructure; the power plant is flexibly mounted for movement as a whole relative to the aircraft structure but the center of a universal joint connecting the power take-off and the power plant remains substantially stationary.

More specifically, it is an object of the invention to provide a resilient mounting systemfor a power plant having a power take-.ofi shaft connected thereto by a universal joint, in which theVv elastic center of the mounting system, or the point of virtual support, is located at a predetermined point en a line passing through the center therotatonal-and translational stiffnesses of the mount system: Aaround and: attheelastic center,

Theseand other objects and advantages of the invention will be pointed out or will become apf parent from-'the following detailed description of one embodiment oftheinvention shown for pury l poses of-illustrationin the accompanying drawing.

, In thefdrawing,

Fig. l shows a side elevation, partly in section,

of an aircraitpower plant and a resilient mounting system-therefor, the mounting system being shown somewhat diagrammatioally and some of the engine cylinders being removed to facilitate illustration;

Fig. 2 is a longitudinal section through a part ofnone of the mount units on an enlarged scale.

In the embodiment of the invention shown in the drawing, an internal combustion vengine power plant it incorporating an engine ofthe multirow, radial type has a orankcase I2 supporting a plurality of cylinders i4 radially arranged Y about the engine crankshaft and enclosed within the engine cowling IS. The crankshaft drives propeller 2li through reduction gearing in the nose section v2l and kdrives a power take-off shaft V22 through an acoessory'shaft in the enginerear section 34. The take-off or extension shaft 22 is connected at one end tothe engine` accessory drive shaft by a universal joint 2Q having its center of universal movement at 0. At its other or aft end shaft 22 is connected to the driveshaft of astationary device or accessory such as an electrical Ygenerator '(not shown) which is fixed to the aircraft structure.

Engine lilis resiliently supported on the fixed' structure of the airplane by a plurality of pedestal type engine mount units generallyindicated ati@ which are of the type. disclosed and claimed in the Tyler and Willgoos application, Serial No.,

579,542, filed February 24, 1945, which is now Patent No. 2,477,501, issued July 26,1943. A plu rality of these engine mount units, for example seven, are disposed at equally spaced` points about theengine and about` a mounting ringv 28 vwhich is connected to Xed `airplane structure. by rigid frame members 3d. To facilitate illustration of the invention, only twoYof-these units are shown in Fig. l..v f

Each` Yengine mount -unit `26 includes a cup shapedfhousing 33 rigidly attached to therear section 3i of the engine by bolts 36 which extend through lugs 3l integral with the housing. EachY The cup shaped housing 32 has an open top closed by a screw threaded cover 46 having a large axial opening 48 through which the smaller hollow stem 50 of a mushroom-shaped core member l freely extends. The annular head 52 of the core member is located in the housing 32, substantially midway between the bottom of the housing and its cover, by resilient rubber pads 54 and 56 bonded to the opposite faces thereof. These pads comprise metal plates 58 and 60 interposed between and bonded to layers of rubber or rubber-like material 59 and 6I. Pad 54 is centered in the cup 32 by the outermost plate 58 which is seated in a shallow recess formed in the bottom surface of the cup. The side walls of the pad are spaced from the walls of the cup. Pad 55, which surrounds the stem 5D and whose side walls are also spaced from the walls of Y the cup, is centered or located by the outermost plate 60 which seats in a pad locating recess formed on the inner face of the cover 45. Stem 5S has a screw threaded axial passage into which is threaded a stud 62 which extends through a sleeve 64 that passes diametrically through and is welded permanently to the mounting ring 28. It will be evident that when the mount unit is assembled', with the stud 62 screwed into the axial passage in the stem 50, the core member 52 isrigidly supported from the ring 28 while the cup 32 and the engine I0 are resiliently supported by the pads `5l! and 55.

A friction mechanism is provided for damping lateral movements of cup 32 relative to core 52. It includes an annular belleville spring member 58, the outer periphery of which ts closely within a recess in the cover 45, cooperating friction member 1D carried by and axially slidable on the stem 50.

In accordance with the present invention, a mounting system is provided for the engine IB, utilizing a plurality of mount units 26, by which a selected point within, or on, the power plant can be maintained stationary during maneuvers of the airplane. For the purpose of explaining the invention, the point O at the rear of the engine has been selected as the point to be maintained stationary, this point being, as illustrated, the center of a universal joint between the engine accessory drive shaft and a shaft 22 which may drive, for example, a generator or a remotely disposed auxiliary-stage supercharger (not shown). It is desirable to maintain the position of the power takeoff at point O stationary with respect to ixed airplane structure regardless of how much motion occurs at other points on the engine with respect t0 the airplane, since the universal joint can withstand angular deilections about O but not lateral deflections.

It has been found that the selected point O can be maintained fixed, without adversely affecting the Vibrational characteristics of the engine in its mount to a material extent, if a definite relationship is maintained between the translational stiffness of the mounting system at the elastic center, the rotational stiffness of the mounting system around the elastic center, and the location of the elastic center with respect to the center of gravity within the power plant and with respect to the point O which it is desired to maintain stationary relative to fixed airplane structure.

By properly arranging the major compressive axesofthe several mount units 25 and selecting suitablev stiiness ratios for Athe mount units, so that the elastic center of the mounting systemV falls on the engine crankshaft at a point inches aft of the center of gravity of the engine and b inches forward of the selected point O, displacement of the point O can be kept at zero during a lateral displacement of the elastic center through a distance :z: inches if 31:61), where e equals the angle in radians through which the engine moves in a counterclockwise direction (Fig. 1) about the point O. The application of power plant weight w, in pounds, will produce deections of =w/lcy and Siwa/ka, where Icy is the translational stiffness at the elastic center in pounds/inch and Ica is the rotational stiness around.- said elastic center in pound inches/radian Substituting these deflections in the equation :15:91) we may write which reduces to the relation ab=k9/Icy. Thus, the point O may be maintained stationary, during a deflection of the power plant as a whole, by correlating the position of the elastic center with the translational and rotational stifnesses of the mount system so that ab-:ks/ky.

Other mount requirements, such as. obtaining a desired frequency spectrumnnust be met in. addition to the one specified above. However, the relative values of lcs and ky, for example, may be varied through a wide range while maintaining the relationship ab=c9/ky. Thus it is possible, within limits imposed by the requirement that lab=kg/ky, to bring the translational and rotational natural frequencies to a satisfactory frequency range. The sum of the distances a and b will be fixed for a given installation by the geometry of the power plant, but the `product ab may be varied by varying a in relation to b to obtain satisfactory translational and rotational frequencies Without upsetting the relationship of the formula ab=Ic@/ky.

In practice may be selected to satisfy some other mountingor vibrational requirement, not directlyconcerned with the present invention. As an ex ample it will be assumed vthat for an installation such as shown in Fig.` 1.-

Also, it will be assumed that a-l-b, for an installation of the type shown in Fig. 1, equals 57,0

should beV equal or substantially equalA to ab. Therefore; if

kan' A is selected as equal, to 225 thenab mustermal,v

225 and if al'b=50, then a canbe taken as, 5 inches and b must equal 45. inches (in this instance it is preferable that c have` the smaller.

value) It can beshown that the` following equationsH apply to mounting systems in whichthe stiff-4 ness of each mount unit: is the saine-jin-fall` shear directions: 1 I

z ku [Sillz a+f 2 1] (2) d d C' Sin a COS a T lSin? a-l-fwhere C=radial distance of mounting unitsfrom crankshaft centerline f f stiffness of individual mounting unit inV cdmpression stiffness of individual mounting unit in shear In the example assumed (for an installation like Fig. 1) C and d, which are determined by the geometry of the installation, are ltaken as equal to 17 inches and 27 inches, respectively.

Hence, substituting:

f-i .Y 4

17 Sin u cos a 2 2 S111 a-I- f l A solution of these two simultaneous equations, to determine values of fr and fa which satisfy the set, may be found in any convenient manner. They are as follows:

C sin a cos a substituting this expression for d-a in b=da+s b C' sin a cos a Sill2 0l Now to obtain the relation of ab=lc9/f/`y in terms of the distance from the C. G. of the power plant to the plane of the mount units. the radial distance of lthe mounting units from the axis of the drive shaft, the stiffness of the individual mounting unit in compression divided by the stiffness of the individual mounting unit in shear, the distance from the plane of the mounting uni-ts to the point O to be held stationary and the angle between the compression axis of each mountingy Unit and the axis of the drive shaft, the expression for'these terms presented in equations (1) (2) and (3) are substituted therein as follows: v f

C'sincosa C'sinacos a-l-s d- 2, 2 I Sint@ Y sina-i-fy 2 2 sinza (sin2 ohh-V) then Sina Orp-z and It will be evident that as a result of this invention it has been made possible to resiliently mount a power plant by means of a plurality of peripherally arranged suspension units so that a selected point on the engine remains stationary with respect to fixed airplane' structure during lateral deflections of the power plant, such as may be caused by maneuver loads applied thereto. While only one embodiment of the invention has been shown and described herein in connection with a power take-off for an engine, it is to be understood lthat the invention is not limited to the particular form shown but may be used in other ways without departure from its spirit as defined by the following claims.

I claim:

1. In combination with aircraft structure, an aircraft power plant having an axial drive shaft, a power takeoff at one end of said shaft including a driven shaft having a universal connection with said drive shaft, and a plurality of flexible mount units connecting said power plant with said aircraft structure, said units being disposed in a plane perpendicular to the axis of said drive shaft and offset from the center of gravity of said power plant, said units having compressive axes intersecting the axis of said drive shaft at a point, the relation of the angle between the drive shaft axis and the respective compressive axes of the mount units to the ratio between the compression stiffness and shear stiffness of the 7 individual mount units being ysuch the equation: ld-(sinza-J-C sinn-cos d where stiifness of individual mounting unit in compression stiffness of individual mounting unit in shear 2. In combination with aircraft structure, an aircraft power plant having an axial drive shaft, a power takeoff at one end of said shaft including a driven shaft having a universal connection with said drive shaft, and a plurality of ilexible mount units connecting said power plant with said aircraft structure, said units being disposed in a plane perpendicular to the axis of said drive shaft and oifset from the center of gravity of said power plant, said units having compressive axes intersecting the axis of said drive shaft at a point offset from said plane, the relation of the angle between the drive shaft axis and the respective compressive axes of the mount uni-ts to the ratio between the compression stiffness and shear as .-to satisfy stiifness of the individual mount units beingsuch as to satisfy the equation:

[C sin a cos rls sin2 a+))]= 2 2 2 sinz a C (yf-Wouw f'` 1 where d=distance from the C. G. of the power plant to the plane of the mount units (the plane containing the centers of the individual moim't-A ing units), s=distance from the plane ofthe mount l units to the center of said universal connections, c=radial distance of mounting units-.from'crankshaft centerline, a=ang1e between compression axes of mounting units and crankshaft axis, and.

f stiiinessof individual mounting unit inecompression stiffness vof'indi-vidual `mount-ing uni-t in shear JOHN M.'TY1ER.

REFERENCES CITED The following references are `of record in the le of 'this patent: 

